1. Field of the Invention
The present invention relates to a rotary electric machine driven by an internal combustion engine which is mounted in a vehicle such as a passenger car, a truck, or boat.
2. Description of the Related Art
As noise has been reduced, requirements for reducing noise of engine accessories has become severe. For example, reduction in noises of an alternator, which always operates while the vehicle is running, is strongly needed. Because the alternator is also required to reduce the weight by reducing the thickness of the housing, which may increase magnetic vibrations, the noise reduction of the alternator has been very difficult.
In general, the magnetic noise is generated when magnetic change in the gap between a stator and a rotor vibrates the stator core, windings and frames supporting the stator core to make an air wave of condensation and rarefaction. It is well known that if the weight of the stator increases, the noises can be reduced.
JP-B-5-50969 proposes to suppress the magnetic vibration of the stator by increasing stiffness of the aluminum frame supporting the stator. However, the aluminum frame can not increase stiffness of the stator directly, and the effect is limited.
JP-A-62-225140 proposes to form a variety of magnetic reluctances in the stator core to moderate the vibration frequency generated in the operation, thereby reducing the magnetic noise. This does not reduce the vibration amplitude, and may vibrate various parts surrounding the alternator. Thus, there was no effective structure for reducing the magnetic noise .
The magnetic vibration of the stator may be generated due to resonation although the amplitude of the vibration is rather small. Such vibration may be transmitted to portions of the stator winding extending from the stator core, which amplify noises.